1. Field of the Invention
The present invention relates to an apparatus and a method for rapidly producing a synthetic gas from a bio-diesel byproduct using microwave plasma, and more particularly, to an apparatus and a method for rapidly producing a synthetic gas, in which, while a plasma flame is generated by a plasma generator and waste glycerin, a bio-diesel byproduct, as fuel, is gasified by being supplied to the generated plasma flame of high temperature, the fuel is supplied in various types to increase the contact time or the contact area with the plasma flame and thus promote gasification thereof and the contents of steam and oxygen supplied and the plasma power are controlled to increase the collection amount of combustible gas and thus allow rapid production of the synthetic gas.
2. Description of the Prior Art
Plasma refers to an ionized state of gas in which atomic nuclei and electrons are separated from each other, which is called the fourth state of matter. The formation of plasma results in generating a large amount of radicals capable of activating a chemical reaction. Plasma may be largely classified into low-temperature plasma and high-temperature plasma.
The low-temperature plasma may be used in a field requiring a chemical reaction at a low temperature of 100° C. or lower. The high-temperature plasma may be applied in fields of incineration, dissolution, and the like, requiring a high temperature since it can raise the material temperature to even 5000° C. or higher for a short time. Recently, the high-temperature plasma technology is studied and applied in fields from simple incineration and combustion to the gasification technology in which the process efficiency is improved and the generated gas is variously utilized. As the plasma method that has been widely used until now, there is a method of using a torch through arc discharge. However, according this method, the electrode lifespan is limited due to a high temperature during discharging, a high power is required since a large amount of current needs to flow, and the electrode lifespan is shortened when steam necessary for a gasification reaction is introduced. Therefore, in recent years, studies on high-temperature plasma application technology utilizing microwaves haven been actively conducted. Particularly, studies on gasification using microwave plasma have gained attention in the arc torch plasma gasification technology that has been much applied to the conventional waste treatment.
Meanwhile, gasification refers to a process that converts hydrocarbon-based materials into a mixed type of combustible gases such as hydrogen, carbon monoxide, and methane, through partial oxidation. With respect to the existing gasification, the apparatus needs to be initially pre-heated to a temperature for operation, about 1300° C. in a manner that the gasification temperature is maintained by using the heat obtained through partial combustion of the fuel. This preheating procedure additively requires a burner, supply fuel, a supply pipe, and other facilities. In addition, the fuel needs to be combusted for a significantly long time since refractory materials of the gasifier need to be also sufficiently preheated. Therefore, an entrained-bed gasifier using coal or the like continuously operates for several months particularly after it is once preheated.
Meanwhile, the plasma gasifier generates plasma to form a flame by using external power, to thereby maintain the reaction temperature, and thus it is not necessary to maintain the temperature through combustion of the fuel. In addition, the plasma gasifier enables the temperature of the central part of the plasma to reach several thousands of degrees for a shot time as compared with the existing gasification manner, and thus has an advantage in that the time necessary for pre-heating is very shot. Further, gasification is carried out in the very high temperature condition, thereby obtaining a short retention time and a high fuel conversion ratio, and a sulfur compound or the like is decomposed by plasma, thereby collecting a clean synthetic gas.
In the existing gasification, the procedure of introducing the fuel into the gasifier has a great deal of influence on the process efficiency. The fuel is atomized and sprayed into the gasifier according to the fuel introduction manner, thereby improving the thermo-chemical conversion efficiency, controlling the retention time in the high-temperature gasification reactor, and facilitating the discharge of unburned ash in the fuel depending on the structure and shape of the gasifier, which are the same for plasma gasification. In the case of microwave plasma, the hydrocarbon fuel needs to be supplied after the plasma generation gas passes through a microwave region to form a plasma flame. Here, the temperature of the plasma is very high at the central part thereof but rapidly decreased toward the periphery thereof. Therefore, there is a technical problem in which the fuel needs to be appropriately supplied to the central part of the plasma. In the lab-scale experiment, a horizontal manner is often used for experimental convenience. In this horizontal structure, hydrocarbon fuel is supplied perpendicularly to flame after the plasma flaming, so that the fuel can be easily supplied to the high-temperature central region of the flame.
In the prior art, fossil fuels such as coal were used as fuel used in the plasma gasifier. However, due to the limitation of mining reserves, oil price fluctuation, and strengthening of CO2 emission regulation, interests and studies on the utilization of new energy sources as an alternative for the fossil fuels are being increased. As for the bio-mass, which is CO2-neutral energy, studies on primary utilization thereof by being combusted to obtain heat and electricity and high value-added utilization thereof by being converted into fuel for transfer, substitutable for petroleum, such as biodiesel, are actively being conducted.
The production amount of biodiesel all over the world has been growing by an average rate of 32.5% each year from 2000 to 2010. The production amount thereof up from 2006 to the present is increasing even more rapidly as compared with that of before 2000. In order to allow the US and the EU to attain their goal of substituting 20% and 30% of petroleum-based diesel with bio-diesel in 2020 and 2030, the production amount of biodiesel is expected to be continuously increased.
With respect to the current main method for producing bio-diesel, alcohol and a catalyst are added to vegetable oil (palm oil, abandoned edible oil, soybean oil, rape seed oil, or the like) and animal oil to allow an esterification reaction, thereby producing fatty acid methyl ester. Here, about 10 wt % of crude glycerin as a by-product is generated. The amount of waste glycerin generated is expected to be increased together with the generation of bio-diesel, and thus effective utilization of the waste glycerin is economically and environmentally important.
Currently, the waste glycerin is thermally used through simple combustion, or treated in a process for energy recovery and thus used in a different field. However, the waste glycerin reacts with steam at a high temperature to generate a synthetic gas containing hydrogen. This principle can lead to production of combustible gas, thermal utilization, production of hydrogen, generation of electricity, utilization as a raw material for various chemical materials, and finally diversification in bio-energy production.
The existing gasifying method not using plasma requires lots of time and energy for pre-heating a reactor. Due to this reason, when the apparatus is once operated, it needs to be continuously operated for several months. Therefore, waste glycerin was difficult to use due to the non-uniform productivity thereof. Whereas, the gasifying method using a plasma torch employs a high-temperature plasma flame and thus requires no time for preheating. Therefore, even though the production of waste glycerin is not uniform and balanceable, it is possible to operate and stop the apparatus anytime. Further, the synthetic gas produced can be rapidly supplied to a market needing combustible synthetic gas.
Accordingly, an apparatus for rapidly producing a combustible gas through a plasma reaction by using high-viscosity waste glycerin as fuel needs to be studied.